1. Field of the Invention
The present invention relates to a chemical and mechanical polishing apparatus. More particularly, the present invention relates to the polishing head of a chemical and mechanical polishing apparatus.
2. Description of the Related Art
Manufacturing an integrated circuit on a semiconductor wafer often includes a chemical and mechanical polishing process used to flatten both surfaces of the wafer. The chemical and mechanical polishing process is becoming more important as semiconductor integrated circuits become more highly integrated and the diameter of wafers become larger.
The chemical and mechanical polishing system used in flattening the wafer comprises a detachable device of a wafer cassette, a wafer transferring device, a polishing device, a wafer rinsing device, and a controlling device. The polishing device comprises a polishing pad, a polishing head for supporting and pressing the wafer against the polishing pad, a polishing plate to which the polishing pad is detachably mounted, a driving mechanism for rotating the polishing head relative to the polishing pad, a device for dressing the polishing pad, a mechanism for rinsing the wafer, and a slurry supplying mechanism.
In the mechanical aspect of the polishing process, the polishing head and the polishing pad are rotated relative to one another at a certain speed, and material at the surface of the wafer is removed by the friction produced between the wafer and the polishing pad against which the wafer is pressed to generate a certain pressure. The rate at which material is removed from the wafer is proportional to the polishing pressure and the polishing speed. In the chemical aspect of the polishing process, a chemical reaction at the wafer surface is produced by slurry introduced between the wafer surface and the polishing pad. If the polishing pressure, the polishing speed, the amount of slurry, the friction between the surface of the wafer and the polishing pad, and the polishing temperature are uniform across the entire surface of the wafer, an extensive flattening and uniformity in the thickness of the residual film are achieved. However, in actuality, the above-mentioned factors and conditions at the surface of the wafer change over time. Accordingly, the thickness of the residual film is irregular after being polished. And, the wafer exhibits dishing and thinning phenomena. Therefore, the polishing conditions must be precisely controlled if the wafer is to be flattened satisfactorily.
Various polishing apparatus and methods have been developed in an attempt to achieve a uniform polishing of a wafer. For instance, Japanese Patent Laid-open No. Hei 10-256202 discloses a polishing method and device in which dual fluid pressure chambers produce a uniform polishing. Japanese Patent Laid-open No. Hei 9-246218 discloses a polishing method and device in which an inflatable pad of polyethylene film is used to uniformly polish a wafer. A polishing device which can regulate the pressures of cells is disclosed in U.S. Pat. No. 5,605,488, and a polishing device in which a wafer is uniformly polished by using a flexible plate is disclosed in U.S. Pat. No. 5,851,136. Finally, U.S. Pat. No. 5,803,799 issued to Volodarsky discloses a polishing head for uniformly polishing a semiconductor wafer.
FIG. 1 shows the polishing head of Volodarsky. The polishing head 10 includes a housing 14, a wafer carrier 20 which is mounted to the housing 14 and has a wafer supporting surface 50, and a wafer retainer 22 which is mounted to the housing 14 and maintains the wafer W on the wafer supporting surface 50. Means are also provided for exerting a biasing force on the wafer carrier 20.
During the polishing process, the wafer W is stuck fast to a polishing pad P by the biasing force applied to the wafer carrier 20. The retainer 22 retains the wafer stuck fast to the polishing pad by the wafer carrier 20. Therefore, the wafer is retained in position and is pressed against the polishing pad by the biasing force distributed thereto via the wafer carrier 20, so that the wafer can be uniformly polished. However, in the polishing head of Volodarsky, it is difficult to distribute the biasing force applied to the wafer carrier 20 uniformly over the wafer.
Accordingly, the worked surface of the wafer is not uniformly stuck fast to the polishing pad, and the central and edge portions of the wafer are polished at different rates.
The present invention has been made in light of the above-mentioned problem of the prior art. Accordingly, it is an object of the present invention to provide a chemical and mechanical polishing apparatus which can uniformly polish a wafer.
In order to achieve the above-mentioned object of the present invention, the present invention provides a polishing head of a chemical and mechanical polishing apparatus for polishing a wafer, which holds a wafer fast against a wafer chuck body of a wafer chucking device, and in such a state exerts a downward uniform pressure on the wafer chuck body to press the wafer uniformly against a polishing pad.
The polishing head includes a housing having air passageways through which air is supplied and/or discharged to and from the polishing head. A carrier is connected to the housing so as to be movable upward and downward relative thereto. The wafer chuck body is, in turn, mounted to the carrier so as to be movable upward and downward relative thereto. A retainer mounted to the periphery of the carrier guides the wafer chuck body in its upward and downward movement relative to the carrier and protects the wafer chucked to the wafer chuck body.
In the present invention, the wafer chuck body and the carrier are independently movable upwardly and downwardly by air pressure. In addition, the wafer chuck body is rotated together with the retainer and the carrier, so that torsion between the carrier and the wafer chuck body is prevented. Therefore, when the wafer chucked by the wafer chuck body is stuck fast to the polishing pad, a surface of the wafer will be polished uniformly.